Titanium and its alloys are used increasingly for surgical devices. Worldwide, more than 1,000,000 partial and total hip and knee replacement prostheses will be inserted per year by 1990, and titanium and its alloy are the metals of choice in the majority of the new implant concepts. Furthermore, dental implants which were introduced in this decade subsequent to the clinically very successful Branemark implant, all rely on this class of metals. The unprecedented rise in the use of this one material system is the result of a widespread belief of excellent in vivo tolerance. Specifically when the local tissue interaction between titanium and the host was analyzed, a favorable histological assessment emerged. Yet, new clinical data as well as recent meticulous biological experimentation revealed unanticipated phenomena that is suggestive of possible adverse reactions. Especially the wear and the histiocytic response associated with joint prostheses and the large specific surface area of the particulate wear debris warrants reaching for a comprehensive understanding of the interaction between titanium based alloys and the physiological environment. This represents the long term objective of this application. It is hypothesized that titanium ions are released in vivo governed by a diffusion mechanism across the oxide that covers the metal. The proof follows from in vitro and in vivo ion release measurements (measured by electrothermal atomic absorption spectroscopy) and the correlation to increases in oxide thickness (measured by angular dependent electron spectroscopy for chemical analysis - ESCA). The second hypothesis is that the released titanium ions accumulate locally and are transported systemically only to a limited extent because of the chemical properties of the released constituents. These data are subsequently used to determine the wear enhanced release effects and quantify the critical stress at which oxide film disruption occurs. The understanding of the relationship between ion release and wear phenomena generated by this study will support the safe use of current titanium based implants, aid in interpreting clinical data and provide a basis for new and improved surgical devices.